1. Field of the Invention
The present invention pertains to a torsion damping mechanism with frictionally connected auxiliary mass.
2. Description of the Related Art
Torsion damping mechanisms are used to reduce variations or peaks in the torque of a drive unit and thus to give the drive shaft behind the torsion damping mechanism a more uniform torque curve. Torsion damping mechanisms of this type are used in clutch mechanisms, for example, and in dual-mass flywheels. A torsion damping mechanism consists of an input area, usually disk-like in shape, on which torque is exerted via the peripheral areas of the one or more disks, and an output area, also usually disk-like in shape, which, in the case of clutch mechanisms, is connected to a hub, which can drive an output drive axle. The disk usually located on the output side is called the hub disk, and it is usually surrounded on both sides by cover plates, which are tightly connected to the torque-transmitting disk on the input side. Torsion damping mechanisms with one cover plate also exist. Dual-mass flywheels do not have cover plates, but they do have comparably functioning elements, namely, a primary flywheel and a cover plate, which is connected to the flywheel. The actual transmission of the torque between the output side and the input side takes place between the cover plate or plates or the flywheel/cover plate combination on the input side and the hub disk on the output side. The two elements are connected elastically to each other by spring-type stored energy elements. Upon rotation of the cover plates or of the flywheel/cover plate combination, special projections on them exert force on the spring elements, which transmit this force in turn to certain areas of the hub disk located at the other end of the spring elements. Thus the cover plates or the flywheel/cover plate combination and the hub disk all rotate around a common rotational axis. Fluctuations in the torque, which are transmitted from the input side drive to the cover plates, are filtered out to a greater or lesser extent by the spring-type stored energy elements, so that the curve of the torque at the output-side hub disk becomes more uniform.
The torsional vibration system in a clutch mechanism, for example, or in a dual-mass flywheel can be described with respect to its critical resonance speed nk as follows:
nk=SQRT((1/J1+1/J2)*c*K)*30/(xcfx80*Z) 
where:
J1 and J2 are the inertias of the primary and secondary side;
c is/are the spring stiffness(es);
K is a correction factor with K+1 if c is given in Nm/rad or with K=180/xcfx80 if c is given in Nm/degree; and
Z is the number of out-of-round events (such as ignitions in an internal combustion engine) per revolution of a drive shaft on the input side.
A disconnection can be achieved only above this rotational speed (starting at SQRT(2)xc3x97nk as a guideline value). In the case of the dual-mass flywheel, the two inertias are approximately the same. Thus the term in parentheses reaches a minimum. In the case of a clutch disk, J1, can have a value of up to 100xc3x97J2. Thus the inertia J2 represents an essential xe2x80x9cleverxe2x80x9d by which the natural frequency of a torsional damping system with a clutch disk can be lowered. The change in the critical speed obtained by shifting the moments of inertia of the term in parentheses, including the root, from the primary to the secondary side is shown in FIG. 12. Point A characterizes here the typical ratio for a dual-mass flywheel, which can be, for example, about 60:40, whereas point B shows the ratio for a typical clutch disk. As can be seen, in the case of the dual-mass flywheel, changes will have hardly any effect because of the very wide minimum. In the case of a clutch disk, however, the resonance point of the system can be changed significantly.
A further improvement in the torque behavior can be obtained by connecting an auxiliary mass (usually by way of a damping element) to the input or to the output side of a torsion damper.
As a result, the mass moment of inertia (MMI) of the output or of the input side is greatly increased, so that at least one natural frequency of the total system is lowered and the so-called supercritical speed range of the drive is significantly increased. It is especially favorable to increase the mass moment of inertia on the output side of a torsion damping mechanism, because the mass moment of inertia is very small here in comparison to the mass moment of inertia on the input side, which means that even a very small amount of additional mass brings about a very sharp increase, in relative terms, in the mass moment of inertia on the output side. The auxiliary mass is preferably connected by way of a damping element. A damping element is preferred which is designed for dry friction, although viscous fluid damping or some other type of damping principle such as magnetic field damping or piezoelectric element damping could also be imagined. The effective friction between the auxiliary mass and the output or the input side can thus be set to any desired value within a wide range.
Especially in the case of clutch mechanisms, torsion damper disks usually have the smallest possible mass moment of inertia, because this must also be synchronized by the synchronizing device in the transmission when the clutch is released and when the gears are shifted. If, under such conditions, the mass of the input side or of the output side of a torsion damper disk is increased even more by adding extra mass, the synchronizing device in the transmission is negatively affected. For this reason, a disconnect device is positioned on the auxiliary mass to disconnect it from the torsion damper disk when the clutch is disengaged, so that the auxiliary mass does not have to be synchronized.
A torsion damping mechanism can be divided into an input side (primary side) and an output side (secondary side). The input side comprises all the elements of the torsion damping mechanism up as far as the spring-type stored energy elements, i.e., all the elements on which an external drive force acts. The output side comprises all the elements which are located on the other force-transmitting side of the spring devices, i.e., the elements which transmit the drive force further onward, including, for example, an output hub which drives an output drive shaft. As a rule, the hub disk is one of the output elements, whereas the cover plates belong to the input side. It is fundamentally possible, however, to reverse the arrangement of these elements, so that the hub disk belongs to the input side, a possibility which is also to be included within the scope of the invention.
An area of application in which torsion damping mechanisms are used includes dual-mass flywheels. These are flywheels which are connected to drives which run irregularly such as internal combustion engines to make them run more smoothly; they are usually installed upline of the clutch. Dual-mass flywheels usually consist of two coaxially aligned flywheels, which are connected to each other by a torsion damper.
In a clutch mechanism, the clutch disk is connected to the cover plates on each side of the torsion damper (or to the hub disk). In the case of conventional dual-mass flywheels, however, these components are replaced by one of the flywheels and a cover plate, all of which therefore are to be referred to as xe2x80x9cside elementsxe2x80x9d in conjunction with the present invention. The side element located on the other side of the hub disk, i.e., the cover element, has a function similar to that of the second cover plate in a clutch mechanism, in that it closes off the entire mechanism, especially the spring-type stored energy elements. In dual-mass flywheels, this second side plate can also have an additional function, namely, to serve as a sealing element in so-called xe2x80x9cwet-runningxe2x80x9d dual-mass flywheels.
The hub disk is connected by appropriate fastening elements such as bolts to the second flywheel.
In many designs, one of the two flywheels of the dual-mass flywheel serves simultaneously as the flywheel of a clutch mechanism, which is connected downline from the dual-mass flywheel.
Previously known added-mass flywheels are designed so that they are connected to the torsion damping mechanism when this mechanism is under load, that is, when a drive on the input side is transmitting a torque to the torsion damping mechanism. Peaks in the torque, which occur when the drive unit is running irregularly, cannot be effectively absorbed in this way and are transmitted to the output side of the torsion damping mechanism.
The present invention is therefore based on the task of providing a torsion damping mechanism with auxiliary mass which is able to damp peak torques.
This task is accomplished by the provision of a torsion damping mechanism having an auxiliary mass which can rotate coaxially with the torsion damping mechanism and which is connected to the torsion damping mechanism by a frictional connection having a frictional moment which, when exceeded during peaks in applied torque, allows the auxiliary mass to slip.
The principle on which the invention is based is to connect the auxiliary mass frictionally to the torsion damping mechanism in such a way that torque peaks are reduced by friction.
The invention therefore pertains to a torsion damping mechanism with a torsion damper with an input side and an output side, where the input side and the output side are connected to each other elastically by spring-type elements for rotation in common. The torsion damping mechanism according to the invention has an auxiliary mass, which can rotate coaxially to the torsion damping mechanism and which is connected frictionally to the torsion damping mechanism by a friction area, where the frictional connection of the torsion damping mechanism to the auxiliary mass has a predetermined frictional moment. When this predetermined value is exceeded such as during the occurrence of peaks in the torque acting on the torsion damping mechanism, the auxiliary mass slips or can slip.
As a result of the auxiliary mass frictionally connected to the torsion damping mechanism, the mass moment of inertia is increased either on the input side or on the output side (depending on whether the auxiliary mass is connected to the input side or to the output side), so that at least one natural frequency of the system is reduced and the supercritical rpm range is thus considerably expanded.
During xe2x80x9cnormal operationxe2x80x9d, that is, without the occurrence of peaks in the torque curve, the auxiliary mass runs with the same rotational velocity as the torsion damping mechanism, because the auxiliary mass adheres to the friction area. When peaks which exceed a predetermined value occur in the torque curve, the frictional torque of the friction area is no longer sufficient to hold the auxiliary mass. The auxiliary mass thus starts to slip, as a result of which relative motion occurs between the friction area of the torsion damping mechanism and the auxiliary mass. This has the effect of dissipating energy, as a result of which the peaks in the torque acting on a drive train into which the torsion damping mechanism according to the invention has been incorporated are capped, and the rotational irregularities are thus reduced.
The influence of an elasticity provided in series with the coulomb friction is preferably kept small in this case, in that the elasticity preferably has a value of at least 100 Nm/degree. In addition, the moment introduced into the auxiliary mass corresponds essentially to the frictional moment acting on the friction area; that is, any elasticity (elastic element) which may be in parallel with the friction between the torsion damper and the auxiliary mass is almost completely excluded.
If desired, the torsion damping mechanism can comprise not only the actual torsion damper itself but also additional elements such as a flywheel or a toothed wheel. In the case of dual-mass flywheels, one of the flywheels is a component of the side elements and can in this case also be considered a part of the torsion damper.
The auxiliary mass is preferably connected by way of a damping element. It is preferable to use a damping element which is designed for dry friction, although viscous fluid damping or some other damping principle such as magnetic field damping or piezoelectric element damping could also be imagined. The effective frictional moment between the auxiliary mass and the output side or the input side can thus be set to any desired value within relative wide limits.
The freedom of coaxial rotation of the torsion damper and the auxiliary mass can be achieved, for example, by providing the auxiliary mass with radial support on a part of the torsion damper such as on a hub or on a flywheel.
Depending on how the auxiliary mass and the torsion damper are arranged, an elastic element which presses the auxiliary mass against the friction area can be provided between the torsion damping mechanism and the auxiliary mass.
The torsion damping mechanism can also have a flywheel arrangement, and the auxiliary mass can be connected by friction to the flywheel arrangement. The flywheel arrangement can preferably belong to the input side or to the output side of the torsion damper.
The flywheel arrangement can, for example, have a flywheel, a cover plate on the flywheel, and a friction plate extending in the radial direction from the cover plate. The auxiliary mass is supported radially on the circumference of the cover plate or of the flywheel, is frictionally connected axially to the friction plate, and is provided with an elastic element acting in the axial direction, which holds the auxiliary mass between the friction plate and the flywheel.
A xe2x80x9cradialxe2x80x9d direction in the present invention is to be understood as a direction which proceeds away from the rotational axis or towards it. xe2x80x9cAxialxe2x80x9d in the sense of the present invention means that the elements are arranged along a line parallel to the rotational axis.
A flywheel arrangement can also be provided on a hub disk, which, for example, can form the central area of a torsion damper (typically surrounded by side elements). In this case, for example, the flywheel arrangement can have a flywheel, which is mounted on the hub disk, and the auxiliary mass can be supported radially on the flywheel so that it extends between the flywheel and the hub disk; the auxiliary mass is frictionally connected axially to the flywheel, and an elastic disk, which presses the auxiliary mass against the flywheel, is provided axially between the auxiliary mass and the hub disk. In this preferred embodiment, therefore, in contrast to the embodiment described previously, the auxiliary mass rubs directly against the flywheel and not against a friction plate provided especially for the purpose. The arrangement of the elastic element also deviates in this case form the previously described design.
In this case, the side elements can have an additional flywheel, which is mounted on either the input side or the output side of the torsion damper, namely, on the side to which the hub disk does not belong. If, therefore, the hub disk is on the input side, the additional flywheel is mounted on the output side and vice versa.
According to another embodiment of the invention, the flywheel arrangement has a first flywheel, which is mounted on a hub disk; the auxiliary mass is supported radially on the first flywheel and extends between the flywheel and the hub disk; and the auxiliary mass is connected axially to the flywheel in a frictional manner. An elastic element, which presses the auxiliary mass against the flywheel, is provided axially between the auxiliary mass and the side of the torsion damper to which the hub disk does not belong, i.e., either the input side or the output side. In this design, therefore, the auxiliary mass is supported by the elastic element on a side of the torsion damper different from that to which it is frictionally connected. If, for example, the auxiliary mass is supported on a flywheel which belongs to the input side, then the elastic element is mounted between the auxiliary mass and the output side.
In addition, the side elements can have a second flywheel on the side to which the hub disk does not belong, which second flywheel extends farther outward radially than the hub disk, the elastic element being located axially between the auxiliary mass and this second flywheel. In this embodiment, therefore, the elastic element and thus the auxiliary mass are supported on the additional flywheel. Because this extends farther outward than the hub disk, the circumferential area of the flywheel is accessible, when looked at from above, because the hub disk does not block it in this embodiment. The elastic element and indirectly the auxiliary mass can thus be supported against this circumferential area of the flywheel.
In another embodiment, the flywheel arrangement can have a first flywheel, which is mounted on a hub disk, and a second flywheel, which is mounted on the other side of the torsion damper. The auxiliary mass is supported radially on the second flywheel, and essentially all of it is radially inside the first flywheel; this auxiliary mass is frictionally connected axially to the first flywheel. In addition, an elastic element is provided, which rubs axially against the auxiliary mass (6) and holds it between the first flywheel (12) and a support element (27) mounted on the first flywheel.
This embodiment differs from those previously described with respect to the support of the auxiliary mass. Whereas, in the previously described embodiments, this mass was always on the side, i.e., either on the input side or on the output side, of the torsion damping mechanism against which the auxiliary mass also rubbed, here, in this embodiment, it is supported on the other side and therefore not on the area to which it is frictionally connected.
The description of the various aspects of the present invention presented above does not include an explanation of how the auxiliary mass can rotate around its support and provides no details on its friction area. One possibility is that the auxiliary mass can rotate freely; that is, it is possible in principle for the auxiliary mass to rotate around a complete 360xc2x0. For certain embodiments, however, it can also be preferable to limit the rotation of the auxiliary mass around its radial support tangentially by stops, with the result that the auxiliary mass cannot rotate around a full 360xc2x0. xe2x80x9cTangentialxe2x80x9d is understood here to mean that points on a plane of rotation which are adjacent to each other in the tangential direction can be converted into each other by rotation. A tangential movement is therefore the movement of a point in a rotational direction which causes no change in its radial distance.
The stops in this case can have at least one stop element, a first area of which is mounted on the torsion damping mechanism, whereas a second area engages with recesses in the auxiliary mass. The tangential ends of the recesses thus limit the relative movement of the stop in the recess. What is present here is therefore a system of grooves, into which a projection can engage but which can move only within the boundaries of the groove.
The first area of the minimum of one stop can be mounted on a flywheel of the torsion damper. If the connection of the auxiliary mass and the attachment of the stops are on the same side of the torsion damping mechanism, the movement of the auxiliary mass is then limited. As a result, the auxiliary mass cannot reach high differential rotational speeds relative to the connected side, so that the amount of energy dissipated by the relative motion is reduced and wear is minimized. If, however, the connection of the auxiliary mass and the attachment of the stops are on different sides of the torsion damping mechanism, the auxiliary mass acts as a carried-along friction ring subject to the mass moment of inertia.
In addition to the advantage described above, the resonance behavior in particular is improved by the additional carry-along friction between the input side and the output side. Thus the first area of the minimum of one stop can be on the flywheel to which the auxiliary mass is not frictionally connected, or the first area of the minimum of one stop can be on the same flywheel as the auxiliary mass.
The torsion damping mechanisms according to the invention described so far can be used in particular as part of a dual-mass flywheel.
In another embodiment, which is especially suitable for clutch mechanisms, the torsion damping mechanism also has an output hub, that is, a hub which, in terms of the direction in which the force is flowing, is downstream from the torsion damper and which serves to transmit the torque to, for example, a transmission. The auxiliary mass in this case is supported radially on this output hub and is frictionally connected axially to the hub disk.
In this embodiment, an elastic element can be mounted radially on the output hub, which element presses the auxiliary mass axially against the hub disk. As already mentioned, the torsion damping mechanism in this case can preferably be a part of a clutch mechanism.
To lower costs, the radial bearing which could be used for the auxiliary mass is located as far as possible radially toward the inside; in particular, it should be radially inside the crankshaft bolts. For this purpose, a drive shaft with a plurality of fastening elements arranged in a circle concentric to the rotational axis can be attached to the side elements or to the hub disk, and the auxiliary mass can be supported radially inside the radius of the fastening elements.
The action of the auxiliary mass depends on the ratio of the mass moments of inertia between the auxiliary mass and the side of the torsion damping mechanism to which the auxiliary mass is connected by friction. In particular, it is preferred that the ratio of the mass moments of inertia between the auxiliary mass and the part of the torsion damping mechanism to which the auxiliary mass is connected be at least 0.1.